Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al₂O₃ ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al₂O₃ film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.     

Tribological Behavior of Electrodeposited Ni-Fe Multilayer Coating

In the present study, the sliding wear behavior of pulse-electrodeposited multilayer Ni-Fe coatings as a function of pulse parameters including frequency and duty cycle has been studied using pin-on-disc tests against an Al₂O₃ counterbody. Sliding wear was investigated with respect to the coefficient of friction (COF), worn surfaces, wear rate, and wear debris. The results of COF with sliding distance revealed a two-region state. At the start of the test the COF was higher, which was due to high stress at the contact region and the occurrence of delamination wear. Then the COF was collapsed as a result of pin penetration and decreased stress at the contact region. The intensity of delamination is decreased at the later stage. The wear resistance of multilayer coatings is increased with increasing frequency and decreasing duty cycles as a consequence of grain refinement and hardness enhancement.     

Effect of CeO2 on the microstructure and wear behavior of thermal spray welded NiCrWRE coatings

NiCrWRE alloy coatings with the addition of CeO₂ were produced on a medium-carbon steel substrate by thermal spray welding. The bonding strength of the coatings was measured by tensile testing and reached 300–350 MPa. The wear behavior of the coatings was investigated under dry sliding wear conditions, and was compared with that of NiCrW coatings produced without the addition of CeO₂. The results show that the hardness and wear resistance of the thermal spray welded coatings are significantly increased with the addition of CeO₂. Analysis of the worn surfaces revealed that the coatings with CeO₂ addition show improved abrasive wear resistance over the coatings without CeO₂.     

Wear study of Ni–WC composite coating modified with CeO2

In the present investigation, Ni–WC composite powder was modified with the addition of CeO₂ in order to form a new composition of Ni–WC–CeO₂. The Ni–WC and Ni–WC–CeO₂ compositions were used for coating deposition by high-velocity oxy-fuel (HVOF) spraying process so as to study the effect of CeO₂ addition on microstructure, distribution of various elements, hardness, formation of new phases, and abrasive wear behavior. Further, the effect of load, abrasive size, sliding distance, and temperature on abrasive wear behavior of these HVOF-sprayed coatings was investigated by response surface methodology. To investigate the abrasive wear behavior of HVOF-sprayed coatings four factors such as load, abrasive size (size in micrometers), sliding distance (meters), and temperature (°C) with three levels of each factor were investigated. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the load, abrasive size, and sliding distance were the main significant factors while load and abrasive size, load and sliding distance, abrasive size and sliding distance were the main significant interactions. Thus an abrasive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modeled and experimental results showed 4–9% error. The abrasive wear resistance of coatings increases with the addition of CeO₂. This is due to increase in hardness with the addition of CeO₂ in Ni–WC coatings.     

Comparative Study of Thermally Sprayed Coatings Under Different Types of Wear Conditions for Hard Chromium Replacement

The tribological properties of part surfaces, namely their wear resistance and friction properties, are decisive in many cases for their proper function. To improve surface properties, it is possible to create hard, wear-resistant coatings by thermal spray technologies. With these versatile coating preparation technologies, part lifetime, reliability, and safety can be improved. In this study, the tribological properties of the HVOF-sprayed coatings WC–17%Co, WC–10%Co4%Cr, WC–15% NiMoCrFeCo, Cr₃C₂–25%NiCr, (Ti,Mo)(C,N)–37%NiCo, NiCrSiB, and AISI 316L and the plasma-sprayed Cr₂O₃ coating were compared with the properties of electrolytic hard chrome and surface-hardened steel. Four different wear behavior tests were performed; the abrasive wear performance of the coatings was assessed using a dry sand/rubber wheel test according to ASTM G-65 and a wet slurry abrasion test according to ASTM G-75, the sliding wear behavior was evaluated by pin-on-disk testing according to ASTM G-99, and the erosion wear resistance was measured for three impact angles. In all tests, the HVOF-sprayed hardmetal coatings exhibited superior properties and can be recommended as a replacement for traditional surface treatments. Due to its tendency to exhibit brittle cracking, the plasma-sprayed ceramic coating Cr₂O₃ can only be recommended for purely abrasive wear conditions. The tested HVOF-sprayed metallic coatings, NiCrSiB and AISI 316L, did not have sufficient wear resistance compared with that of traditional surface treatment and should not be used under more demanding conditions. Based on the obtained data, the application possibilities and limitations of the reported coatings were determined.     

Friction and Wear Behavior of WS2/Zr Self-lubricating Soft Coatings in Dry Sliding Against 40Cr-Hardened Steel Balls

WS₂ and WS₂/Zr self-lubricating soft coatings were produced by medium-frequency magnetron sputtering, multi-arc ion plating and ion-beam-assisted deposition technique on the cemented carbide YT15 (WC + 15 % TiC + 6 % Co) substrates. Microstructural and fundamental properties of these coatings were examined. Sliding wear tests against 40Cr-hardened steel using a ball-on-disk tribometer method were carried out with these coated materials. The friction coefficient and wear rates were measured with various applied loads and sliding speeds. The wear surface features of the coatings were examined using SEM. The results showed that the WS-1 specimen (with WS₂/Zr composite coating) has higher hardness and coating/substrate critical load compared with that of the WS-2 specimen (only with WS₂ coating). The friction coefficient of WS-1 specimen increases with the increase in applied load and is quite insensitive to the sliding speed. The wear rate of the WS-1 specimen is almost constant under different applied loads and sliding speeds. The WS-1 specimen shows the smallest friction coefficient and wear rate among all the specimens tested under the same conditions. The WS-1 specimen exhibits improved friction behavior to that of the WS-2 specimen, and the antiwear lifetime of the WS₂ coatings can be prolonged through adding Zr additives. The self-lubricating and wear mechanism of the WS₂/Zr coating was also found from the sliding wear tests.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Wear Behavior of Thermally Sprayed Coatings under Different Loading Conditions

Wear behavior of three kinds of thermally sprayed coatings with similar hardness have been investigated under steady-state and dynamic loading tests. The steady-state loading tests were conducted on a reciprocating sliding device and the dynamic loading tests were conducted with a single-pendulum scratching device. Experimental results show that the wear mechanisms of the coatings under steady-state sliding friction testing are microcutting and microploughing, whereas the material losses under the dynamic impact scratch testing are mainly due to split cutting and fracture. Tribo-oxidization in the sliding process was found to have an influence on the wear behaviors of the thermally sprayed coatings. The results also indicated that wear resistance of thermally sprayed coatings can be correlated to hardness, plasticity, toughness, and cohesion. As far as the coatings of similar hardness were concerned, the wear resistance under steady-state loading was mainly due to the cohesion of the laminar structure of the coatings and the wear resistance under dynamic loading was mainly due to the toughness and deformation compatibility of the coatings.     

Influence of Heat Treatment on Microstructure and Sliding Wear of Thermally Sprayed Fe-Based Metallic Glass Coatings

Fe₆₂Ni₃Cr₄Mo₂W₃Si₆B₁₇C₃ amorphous coatings were thermally sprayed by a high velocity oxygen fuel spraying system (DJ-2700) and heat-treated at the temperatures ranges from 873 to 1,173 K in vacuum for 1 h. Differential scanning calorimetry, X-ray diffraction (XRD), and scanning electron microscopy were used to study the microstructural characteristics of the coatings. Vickers hardness tester was used to measure the hardness of the coatings. At the same time, the sliding wear behavior of the coatings was evaluated in a reciprocating ball-on-disk system. Within the resolution of XRD, amorphous structure without apparent crystalline phases was obtained in the as-sprayed coating. The heat treatments above 873 K led to the crystallization of amorphous phase. With the increase of heat treatment temperature, diffusion and sintering could occur between the layers of the coatings. The highest microhardness was obtained in the coating heat-treated at 973 K. When wear tested at a relative low load of 2 N, a direct correlation between the hardness and wear resistance of the coatings seems to be reasonable. However, at relative high loads, the wear resistance of the coatings is dependent on the resistance to crack initiation and growth between the layers rather than the hardness.     

Third Body Behavior During Dry Sliding of Cold-Sprayed Al-Al2O3 Composites: In Situ Tribometry and Microanalysis

Reciprocating sliding wear experiments were conducted on cold-sprayed pure aluminum and Al–22.6 wt% Al₂O₃ coatings using a custom-built in situ tribometer. Using a transparent sapphire counterface for the wear tests, the dynamic behavior of third body material in the contact was optically observed. The presence of Al₂O₃ particles led to greater stability of the transfer films adhering to the sapphire counterface, as well as greater stability of the friction coefficient and lower wear rates. Ex situ microanalysis of material in the wear tracks and transfer films suggests that the presence of Al₂O₃ particles promoted strain localization during sliding. This produced more uniform third body microstructures and protected the underlying aluminum matrix from deformation, which slowed the rate of transfer to the counterface.     

Microstructure and Dry-Sliding Wear Behavior of Thermal Sprayed and Fused Ni-Based Coatings with the Addition of La2O3

A Ni-based alloy with 1.5 wt% of La₂O₃ powders was thermal sprayed onto steel substrate. The microstructure and dry sliding wear behavior of the coatings were studied by XRD, field emission gun scanning electron microscope (FEGSEM) and SEM analyses. The microstructure of the coating with 1.5 wt% of La₂O₃ differs widely from the coating without La₂O₃; the typical microstructure with 1.5 wt% of La₂O₃ is composed of net-like dendrite (Cr, Fe)₂₃C₆ and Cr₇C₃, cellular-dendrite Fe₂₃(C, B)₆, γ-Ni + Ni₅Si₂ interdendritic lamellar eutectic. Interestingly, significant amounts of net-like (Cr, Fe)₂₃C₆ and Cr₇C₃ hard phases as a wear-resistant skeleton were formed and uniformly dispersed in the coating. Meanwhile, blocky and rod-like hard-phase CrB scattered in the coating can also contribute to improving the wear resistance. The novel microstructure, therefore, is beneficial for wear resistance. Friction and wear tests without lubricant show that the friction coefficients of the coating are less than 0.57. There is an approximately linear relationship between friction coefficients and sliding speed. The wear rate slightly increases with an increase of load, and the wear rate of the coating slightly decreases with sliding speed.     

Tribological properties of plasma sprayed and laser remelted 75/25 Cr3C2/NiCr coatings

A CO₂ laser was used to fuse based Ni–Cr Cr₃C₂ coatings for the purpose of homogenizing their microstructures and eliminating their porosity. Tests of layer control and wear resistance were carried out on the samples treated with the laser. The results have shown that laser remelting improves the microstructure of the coatings, increases the coating microhardness, and improves coating–substrate adherence. The dry sliding wear behaviour was characterized by the existence of two periods. During the first period the square of the wear volume is proportional to the sliding distance. During the second, the wear volume is proportional to the sliding distance.     

TiSiC,TiSiC-Zr,and TiSiC-Cr Coatings—Corrosion Resistance and Tribological Performance in Saline Solution

TiSiC coatings alloyed with Zr and Cr were deposited on Si and 316 L steel substrates by a cathodic arc method in a CH₄ reactive atmosphere. The corrosion and wear behavior of the coatings in 0.9% NaCl solution was investigated. Corrosion resistance of the coatings was evaluated by electrochemical tests. The electrochemical polarization measurements were conducted at room temperature in the potential range ?1 and 1.5 V, with a 0.167 mVs^?1 scan rate. Compared to the uncoated 316 L substrates, the coated ones showed nobler characteristics, with more electropositive corrosion potentials, lower corrosion current densities, and higher polarization resistances. TiSiC-Zr exhibited the lowest corrosion current density (0.62 μAcm^?2) and the highest protection efficiency (69.5%). The tribological performance of the coatings under corrosive conditions (0.9% NaCl solution) was investigated using a ball-on-disc tribometer (6-mm-diameter sapphire ball, 5 N load, 0.15 ms^?1 sliding speed, 400 m sliding distance). The TiSiC-Cr coating demonstrated the best wear behavior, with a wear rate of 3.2 × 10^?6 mm³N^?1m^?1, followed by TiSiC and TiSiC-Zr. The morphologies and compositions of the worn surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) in order to identify the wear mechanism. Corrosion, debris adhesion, and oxidation were found to be the dominant wear processes.     

Sliding and abrasive wear behaviour of boride coatings

Polyphase boride coatings constituted by an inner layer of Fe₂B and an outer layer of FeB were thermochemically grown on iron and medium carbon steel by a pack cementation process. The tribological behaviour of borided samples was investigated under both sliding and abrasion testing conditions. Considerably different values of wear rate were found in different regions of the coatings. The differences were explained on the basis of the crystallographic order of iron borides. The resistance to both types of wear was initially poor due to the presence on the coatings of a thin, friable layer constituted by disordered crystals. Then the resistance increased to a maximum value in regions constituted by compact, highly ordered crystals of Fe₂B. The resistance to dry sliding of borided samples was better than that displayed by samples submitted to alternative surface treatments (e.g. gas nitriding) and lower that that measured for a WC-Co hard metal coating.     

Preparation,microstructure and tribological behavior of laser cladding NiAl intermetallic compound coatings

Nickel aluminide (NiAl) intermetallic compound coatings were in situ synthesized from pre-placed mixed powders of Ni and Al by laser cladding. The phase composition and microstructure of the NiAl coatings were studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of laser cladding parameters on the microstructure and friction and wear behavior of the NiAl coatings were investigated. It has been found that laser power density had a crucial influence on the microstructure and friction and wear behavior of NiAl coatings. Namely, the NiAl coatings synthesized under a lower power density have more dense and fine microstructure, and lower friction coefficient and wear rate. Besides, the friction and wear behavior of the laser cladding NiAl coatings is highly dependent on applied normal load and sliding speed; and the resulting coatings sliding against Si₃N₄ in a ball-on-disc contact mode is more suitable for tribological application at a moderate normal load of 3–7 N and sliding speed of 0.16–0.21 m/s.     

Tribological behaviour of plasma sprayed Al2O3 and TiO2 ceramic hard coatings under dry contact

Plasma sprayed ceramic coatings are used in a number of industries in which surface modification of components to compare tribological properties is important: so hence, are evaluations of their tribological properties. This paper presents a study on the wear behaviour of three ceramic coatings — Al₂O₃, TiO₂ and Al₂O₃-TiO₂combination — in the load and speed ranges of 5 to 50 N, and 0.3 to 10 m/s, respectively, on which few data are available in the literature. The tests were carried out using a standard dry sand rubber wheel abrasion test and a pin-on-disc machine under dry sliding conditions. It was found that a stick-slip effect seems to occur at low sliding speeds, and transition takes place at a sliding speed of around 4 m/s. Of the three ceramic coatings, TiO₂ was found to be the most wear resistant, with the least friction coefficient, although it is less hard than the Al₂O₃ coatings. Scanning electron microscopy of the surface shows evidence of wear mechanisms such as plastic deformation, transfer-film formation, micro cracks, and grain pull-out in the coatings.     

High Wear Resistance of Magnetron Sputtered Cr<Subscript>80</Subscript>Si<Subscript>20</Subscript>N Nanocomposite Coatings: Almost Independent of Hardness

Hardness has been popularly considered as an essential factor defining the wear resistance of hard coatings. Here, we report magnetron sputtered Cr₈₀Si₂₀N nanocomposite coatings, of widely varied packing densities, that exhibited identical specific wear rates, while the hardness changed over a wide range (from ~12 to ~36 GPa). All the Cr₈₀Si₂₀N coatings were free of extended and uninterrupted columnar boundaries, and retained low specific wear rates in the ball-on-plate sliding tests against Al₂O₃ counterpart with a normal load of 5 N (less than 3.0?×?10^?16 m³/N m under ambient condition and less than 2.0?×?10^?15 m³/N m under 3.5 wt% NaCl solution, respectively). Post examination reveals extensive interruption or termination of cracks in the wear tracks of the under-dense coatings, indicative of extrinsic toughening mechanisms by effective relief of local contact stress. Our results suggest that a critical role of toughening rather than hardening, played in enhancing the wear resistance of hard coatings, and thus would pave a way to develop highly wear-resistant coatings with a low hardness.     

Sliding wear behaviour of ZrN and (Zr, 12 wt% Hf)N coatings

In the present study, the sliding wear resistances of ZrN and (Zr, 12 wt% Hf)N coatings deposited on a hardened AISI D2 tool steel by arc-physical vapor deposition (PVD) technique were examined by a ball-on-disc wear tester. Alloying of ZrN coating with 12 wt% Hf did not change the hardness significantly, but achieved an improvement on adhesion strength and dry sliding wear resistance against steel (AISI 52100-55HRC) and Al₂O₃ balls.     

Effects of CeO2 on friction and wear characteristics of Fe–Ni–Cr alloy coatings

The effects of rare earth oxide CeO₂ on the microstructure and wear resistance of thermal sprayed Fe–Ni–Cr alloy coatings were investigated. The powders of Fe–Ni–Cr alloy with the addition of CeO₂ were flame sprayed on to a 1045 carbon steel substrate. The coatings were examined and tested for microstructure feature, compositions, and phase structure. Tribological properties of coatings were tested under reciprocating sliding test. The results were compared with those for coatings of the alloy without CeO₂. The comparison indicated that the addition of rare earth oxide CeO₂ could refine and purify the microstructure of coatings, and increase the microhardness of the coatings. As a result, by CeO₂ addition, the friction coefficient of the coatings was decreased slightly and the wear resistance of the coatings was enhanced significantly.     

Study of tribological performance of ECR-CVD diamond-like carbon coatings on steel substrates: Part 1. The effect of processing parameters and operating conditions

Diamond-like carbon (DLC) coatings were prepared on AISI 440C steel substrates at room temperature by electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma. Using the designed Ti/TiN/TiCN/TiC interfacial transition layers, relatively thick DLC coatings (1-2 μm) were successfully prepared on the steel substrates. The friction and wear performance of the DLC coatings was evaluated by ball-on-disk tribometry using a steel counterbody at various normal loads (1-10 N) and sliding speeds (2-15 cm/s). By optimizing the deposition parameters such as negative bias voltage, DLC coatings with hardness up to 30 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball could be obtained. The friction coefficient was maintained for 100,000 cycles (∼2.2 km) of dry sliding in ambient environments. In addition, the specific wear rates of the coatings were found to be extremely low (∼10⁻⁸ mm³/Nm); at the same time, the ball wear rates were one order of magnitude lower. The influences of the processing parameters and the sliding conditions were determined, and the frictional behavior of the coatings was discussed. It has been found that higher normal loads or sliding speeds reduced the wear rates of the coatings. Therefore, it is feasible to prepare hard and highly adherent DLC coatings with low friction coefficient and low wear rate on engineering steel substrates by the ECR-CVD process. The excellent tribological performance of DLC coatings enables their industrial applications as wear-resistant solid lubricants on sliding parts.